The use of granular activated carbon (GAC) for water purification became common around the start of the 20th century (1906) when the
“activation” process was applied to charcoal (which had been used for centuries). Thermal activation of charcoal greatly improves its pore volume, surface area and structure making it a superb workhorse for water treatment.[u]yrdcarbon[/u] A clean carbon surface is oleophilic, meaning
“oil loving” and the opposite of hydrophilic or “water loving”. It has a strong attraction for organic compounds and other non-polar contaminants and adsorbs them onto the carbon surface where they are held by van der Waals forces. Adsorption is the primary mechanism by which GAC works and the primary reason it is widely used to reduce undesirable taste, odor and color and to improve the safety of drinking water by also effectively removing common disinfection byproducts (THMs), organic contaminants like chlorinated solvents and other industrial pollutants, pesticides, and select heavy metals such as lead and mercury. , Modern GAC products are made from coconut shell, coal, wood, lignite and/or petroleum products. The selection of carbon source is often driven by the contaminant reduction performance targeted by the manufacturer. Each carbon source produces a GAC with a unique pore structure consisting of micro-pores, mesopores and macro-pores. Micro-pores are very small
—often smaller than a typical molecule (5-1000 Angstroms). An Angstrom (?) is 1/10,000,000 of a millimeter. As an illustration, the period at the end of this sentence is about 5,000,000 ?. Coconut shell carbons tend to have a higher percentage of micro-pores making it a good choice for small organics and disinfection byproducts. Wood carbons have more macro-pores making them better for de-colorization and removal of larger organics. Coal bases give an intermediate pore structure making them a good choice for general purpose organic reduction.
GAC
’s capacity for organic removal is derived from its very high surface area. A single gram of GAC can have a surface area exceeding 1000 m2 . A pound of carbon has more than 35 acres of surface— almost 100 football fields. It is not possible to utilize the complete surface area of GAC nor is it necessary. If you were to load a one molecule thick, filmed layer of an organic onto the entire surface of GAC, you would have only loaded about 6.25 ml of liquid~~ about 1/4 teaspoon per pound. But since the organic is soluble in itself, the film thickens and the adsorbed weight increases. With systems in series and running to saturation (outlet contaminant level equals inlet level) it is possible to load as much as 0.1 lbs or 45 ml on a volumetric basis per pound of GAC.[u]activated carbon pellets manufacturer[/u]
